The present invention relates generally to electric machines and, in particular, to a stator for an electric machine having a core and a winding. Electric machines, such as alternating current electric generators, or alternators are well known. An automotive alternator is an electric machine which charges the battery of an automotive vehicle. Prior art automotive alternators typically include a stator assembly and a rotor assembly disposed in a alternator housing. The stator assembly is mounted to the housing and includes a generally cylindrically-shaped stator core having a plurality of slots formed therein. The rotor assembly includes a rotor attached to a generally cylindrical shaft that is rotatably mounted in the housing and is coaxial with the stator assembly. The stator assembly includes a plurality of wires wound thereon, forming windings. The stator windings are formed of slot segments that are located in the core slots and end loop segments that connect two adjacent slot segments of each phase and are formed in a predetermined multi-phase (e.g. three, five, or six) winding pattern in the slots of the stator core.
The rotor assembly can be any type of rotor assembly, such as a “claw-pole” rotor assembly, which typically includes opposed poles as part of claw fingers that are positioned around an electrically charged rotor coil. The rotor coil produces a magnetic field in the claw fingers. As a prime mover, such as a steam turbine, a gas turbine, or a drive belt from an automotive internal combustion engine, rotates the rotor assembly, the magnetic field of the rotor assembly passes through the stator windings, inducing an alternating electrical current in the stator windings in a well known manner. The alternating electrical current is then routed from the alternator to a distribution system for consumption by electrical devices or, in the case of an automotive alternator, to a rectifier and then to a charging system for an automobile vehicle including a battery.
One type of device is a high slot fill stator, which is characterized by rectangular shaped conductors whose width, including any insulation fit, closely to the width, including any insulation of the rectangular shaped core slots. High slot fill stators are advantageous because they are efficient and help produce more electrical power per winding than other types of prior art stators. A disadvantage of the high slot fill stators is the difficulty of inserting the wires whose width fits closely to the width of the slots. After the windings have been placed within the core slots, there is a possibility of the winding falling out of the core slots. Sometimes, a varnish is applied to secure the windings within the core slots. The process and tooling required to apply the varnish is complex and adds significant cost to the manufacturing of the core. It is difficult to use tooling to hold the wires in the core slots during the application of the varnish and therefore it is desirable to add a feature to the stator assembly to trap the wires in the core slots prior to the varnish operation it is also well known that the magnetic reluctance in the airgap between the rotor and the stator is proportional to the power output of the electrical machine. The reluctance in the airgap refers to the magnetic resistance that the magnetic field encounters when crossing the gap from the rotor and stator. Increasing the amount of core teeth area that overhangs the adjacent rotor pole finger can reduce the reluctance of the gap. Therefore, wider faces on the ends of the core teeth reduce the magnetic reluctance in the air gap and increase the power density of the machine.
It is also known that there is a substantial amount of power loss on the surface of the pole fingers due to eddy currents passing through the steel causing heat. These eddy currents are generated by variations in induced voltages in the steel caused by flux density variations and changes on the pole surface as it rotates under the stator core teeth. Wider core teeth help to reduce the amount of flux density variation on the pole finger face and, therefore, result in lower power loss due to eddy currents. Therefore, wider faces on the ends of the core teeth reduce the eddy current losses on the pole finger faces.
It is desirable, therefore, to provide a stator assembly that meets the requirements of a high slot fill stator including conductors having slot segments with a width, including any insulation, that closely fits to the width, including any insulation, of the core slot, and being radially inserted into a cylindrically-shaped core and being secured therein.